Abstract – Magnetite (Fe304)/polyaniline core–shell composites were synthesized using a reactive surfactant to improve magnetite dispersion and as the monomer of conducting polyaniline. Reduction of magnetic particle aggregation and core-shell morphology were evidenced by electron microscopy. Additionally, the decrement in magnetization (r) and (hysteresis) Hc observed in the core–shell composite was be attributed to the increment in dipolar magnetic interaction due to the increased separation among the Fe3O4 nanoparticles because of the PAni shell formation.